This invention relates to the production of control signals for operating a visual display mechanism of the scanning type, such as a standard television receiver, and, more particularly, to a method and apparatus for inexpensively producing scanning control signals which provide a high resolution display and can be easily changed from display to display. The invention accomplishes this by composing under the control of a microprocessor each frame of a display substantially simultaneously with the time the display surface is being scanned to produce the same.
Until recently, standard television receivers of the type found in homes and places of congregation throughout the developed countries have been passive elements. That is, standard television receivers are used traditionally only to display programming transmitted to the same from an image pick up device, such as a camera. Television receiver control units are now available, however, which turn TV receivers themselves into active instrumentalities, i.e., instrumentalities in which the viewer can directly control or influence the actual display which is on the receiver screen at a given time. Such control units are typically designed for use of the television receiver as a game display, such as a display of a modified version of the game of ping-pong. The viewer becomes a participant in such a game by manipulating the screen display, which display may be programmed to react to the control in a particular way. For example, in the modified game of ping-pong the viewer or participant can move a paddle on the screen to intercept a ball. The ball will react to the interception by "bouncing" from the paddle with an appropriate deflection angle.
There are basically two different kinds of TV receiver control units of the game type. One is the so-called hard-wired type which includes specific logic designed to perform a particular function, such as play a particular game. Hard wired control units are quite limited in their use. That is, not only are such units limited to specific games, economics limits the same to quite simple games. Moreover, the amount of hardware required to provide a highly resolved visual display with multiple movements on TV receiver is more than what can be provided economically.
The other type of control unit now available utilizes a microprocessor as a primary component in order to gain the versatility inherent in such a device. Presently available ones, however, do not take full advantage of the resolution, color and movement capabilities of standard television receivers. For example, each frame of TV receivers built in accordance with the NTSC scanning standards adopted in the United States and Japan will be made up of 483 individual horizontal scan lines. Each scan line includes about 320 individual display points, each one of which can be individually defined. This means that on a standard 19 inch television screen, "dots" which are only about 47 mils apart, center-to-center, can be individually programmed to obtain good resolution.
The approach taken by most microprocessor-based control units now available is to duplicate or, in other words, "map" in a memory information defining a frame which is to be displayed, which information is then read out to the television receiver to control its display. It will be recognized that an inordinate and quite expensive amount of memory would be required to individually specify in the "map" different information for each one of the "dots" which individually can be generated by a TV scanning system. This is particularly true if a color display is generated. The information needed to specify each of the dots then must include color information, as well as intensity information. Because of this, it is the practice now to generate much larger, single color dots to make up a display, with the concommitant result that the resolution is likewise reduced.
The memory mapping concept now used to define the frames of a display results in another major limitation on presently available devices using microprocessors. Any appreciable object movement between frames requires that the content of the memory be altered, copied, exchanged or deleted. Thus, the step of moving an object in the display can be quite demanding on a microprocessor and is awkward to execute, particularly in the relatively short time, about 1.3 milliseconds, between fields.